A powered subwoofer is completely self-contained, with the internal amplifier matched to the specifications of the driver. There is no correlation between your receiver and subwoofer as far as impedance is concerned, so you can purchase whichever unit you'd like. Thank you for the explanation! As you can see, I'm clueless and had spent my Physics class hours playing games. So... if a speaker is not self-powered, it should match the Ohms specs of receiver, if it is self-powered, don't worry about getting your receiver fried.